The reduction of emissions from diesel engines has been one of the primary elements in obtaining air quality and greenhouse gas reduction goals within California and throughout the nation. A key element of the California Air Resources Board’s (CARB’s) efforts in reducing greenhouse gases over the past few years has been the implementation of the Low Carbon Fuel Standard (LCFS), the goal of which is to reduce carbon intensity of transportation fuels by 10% by 2020. This will predominantly be achieved by introducing more renewable fuels to partially replace conventional fuels for transportation applications.
Biodiesel is a renewable fuel that has the potential for diesel fuel applications, but there is a tendency for biodiesel to increase NOx emissions, which remains an important issue with respect to implementing biodiesel within California. In order to determine whether increased levels of biodiesel use within the State of California would affect air quality, CARB conducted an extensive study on the emissions impacts of biodiesel use. The results of this study showed that B20 and higher biodiesel blends would likely increase NOx emissions in CARB diesel fuels. The potential impact of lower level biodiesel blends, such as B5, on NOx, on the other hand, was unclear, showing increases in some cases, but not in others. A subsequent study found increases in NOx for a B5 soy-based and waste vegetable oil (WVO) biodiesel, but either no increases or a slight reduction for a B5 animal based biodiesel.
The goal of this study was to conduct a more comprehensive study of the emissions impacts of lower level B5 and B10 blends in CARB diesel fuel. For this study, B5 and B10 biodiesel blends with both an animal-based and a soy-based biodiesel feedstock were tested. These fuels were tested in a 2006 Cummins ISM engine and a 1991 Detroit Diesel Corporation (DDC) Series 60 Engine over the standard Federal Test Procedure (FTP), the Urban Dynamometer Driving Schedule (UDDS), and the Supplemental Emissions Test (SET).
NOx emissions results for the testing of the 2006 Cummins ISM engine showed a statistically significant 1.0% and 1.9% increase, respectively, for the B5-soy and the B10-soy blends compared to the CARB diesel fuel for the FTP cycle, and a statistically significant increase of 3.6% for the B10-soy blend compared to the CARB diesel fuel for the UDDS. NOx emissions for the 1991 DDC Series engine showed a statistically significant increase of 1.0% and 3.2%, respectively, for the B5-soy blend for the FTP and UDDS cycles. Similarly, the B10-soy blend showed a statistically significant increase of 1.5% and 1.3%, respectively, for the FTP and SET cycles. NOx emissions for the animal biodiesel blends did not show the more consistent NOx increases found for the soy biodiesel blends, with only the B10-animal blend showing a statistically significant increase of 0.7% for the FTP on the 1991 DDC engine.